1. Field of the Invention
This invention relates to an apparatus for controlling the drop-wise flow of a fluid material such as liquid medication, a physiological salt solution or blood, wherein the fluid flows in the form of free-falling drops under the influence of gravity. More particularly, the invention relates to improvements in an apparatus of the type described, in which the initial conditions for the control of the fluid drop-rate are established in a short period of time.
2. Description of the Prior Art
In intravenous feeding or blood transfusions it is necessary to maintain a preset drop-rate of fluid in a drop chamber. In order to control the fluid flow automatically, it is conventional practice to drive a pinch clamp by means of a cam coupled to a motor, whereby the diameter of the tubing connected to the drop chamber is adjusted to set the desired drop-rate. A factor which must be taken into consideration in the automatic clamping operation is a delay in the dropping of the fluid caused by the air pressure within the drop chamber and the resistance offered by the flow channel. The delay phenomenon causes the drop-wise feed of the fluid to lag behind the clamping action of the pinch clamp, and causes the feed rate control operation to start only after the pinch clamp has allowed the tube diameter to expand to an excessive degree. This results in a drop-rate which is outside the appropriate limits, and makes it necessary to increase the clamping force to back up to the zero-set position where there is complete cut off of the flow passage. The only way to avoid this inconvience has been to pass the point of zero flow-rate, determined by the pinching action of the clamp, at an extremely slow speed. Moreover, the point of zero-flow rate, namely the desired initial condition from which control of the fluid flow starts, is not a constant value every time as it is decided by the wall thickness and flexibility of the tubing, which may differ from one apparatus to the next. Accordingly, it has heretofore taken an excessively long time to establish the initial clamping conditions of the pinch clamp.